Carbon fiber aggregate and method for producing same, and electrode mixture layer for nonaqueous-electrolyte secondary battery

Abstract

With the present invention a carbon fiber aggregate is provided that has an average fiber diameter of 100-1000 nm, and a fiber diameter variation coefficient (CV value) greater than 0.5 and less than or equal to 1.0.

The invention claimed is: 
     
       1. A carbon fiber aggregate with an average fiber diameter of 100 to 1000 nm, an average fiber length of 10 to 30 μm, and a coefficient of variation (CV value) of the fiber diameter of greater than 0.50 and 1.0 or less. 
     
     
       2. The carbon fiber aggregate according to  claim 1 , wherein the carbon fiber aggregate has a crystallite spacing (d002) in accordance with an X-ray diffraction method of 0.3400 nm or more. 
     
     
       3. The carbon fiber aggregate according to  claim 1 , which has a tap density of 0.020 to 0.100 g/cm 3 . 
     
     
       4. The carbon fiber aggregate according to  claim 3 , wherein a bulk density measured in a pressurized state at a pressure of 3.0 kg/cm 2  is 5.0 to 30 times the tap density. 
     
     
       5. The carbon fiber aggregate according to  claim 1 , wherein powder volume resistivity A (Ω·cm) when packed with a packing density of 1.5 g/cm 3  is 7.0 to 20% of powder volume resistivity B (Ω·cm) when packed with a packing density of 0.50 g/cm 3 . 
     
     
       6. The carbon fiber aggregate according to  claim 3 , wherein a bulk density measured in a pressurized state at a pressure of 1.5 kg/cm 2  is 2.0 to 15 times the tap density. 
     
     
       7. An electrode mixture layer for a nonaqueous electrolyte secondary battery, comprising:
 the carbon fiber aggregate according to  claim 1 ; and an electrode active material. 
 
     
     
       8. A method for producing the carbon fiber aggregate according to  claim 1 , comprising:
 (1) a fiberizing step of forming a resin composition composed of a thermoplastic resin and 30 to 150 parts by mass of a mesophase pitch based on 100 parts by mass of the thermoplastic resin, in a molten state, thereby fiberizing the mesophase pitch to obtain a resin composite fiber; 
 (2) a stabilizing step of stabilizing the resin composite fiber to obtain a resin composite stabilized fiber; 
 (3) a thermoplastic resin removing step of removing the thermoplastic resin from the resin composite stabilized fiber to obtain a stabilized fiber; and 
 (4) a carbonizing and firing step of heating the stabilized fiber under an inert atmosphere for carbonization or graphitization to obtain a carbon fiber aggregate. 
 
     
     
       9. The carbon fiber aggregate according to  claim 2 , which has a tap density of 0.020 to 0.100 g/cm 3 . 
     
     
       10. The carbon fiber aggregate according to  claim 9 , wherein a bulk density measured in a pressurized state at a pressure of 3.0 kg/cm 2  is 5.0 to 30 times the tap density. 
     
     
       11. The carbon fiber aggregate according to  claim 9 , wherein a bulk density measured in a pressurized state at a pressure of 1.5 kg/cm 2  is 2.0 to 15 times the tap density.